An automatic warehousing arrangement including racks and a handling apparatus has been known, as described in, for example, Japanese Patent Application Laid-Open No. 63-218407. In this known arrangement, the handling apparatus or a crane comprises a lower frame, a pair of guide posts, front and rear, upstanding from the lower frame and spaced in the direction of back and forth movement of the crane, an upper frame interconnecting the top ends of the guide posts, and a vertically movable carriage guided along the guide posts. The vertically movable carriage carries a transfer device, such as a fork.
The posts have guide rail portions of an open groove shape formed on inwardly opposed surfaces thereof. The vertically movable carriage is provided at its front and rear ends each with a movable shaft urged by a spring for projection outward. Mounted to each movable shaft are a first guide roller for inhibiting longitudinal oscillations which contacts the bottom of the corresponding guide rail portion, and a second guide roller for inhibiting lateral oscillaions which is opposed to sides of the guide rail portion. Each post is hollow in its interior, the hollow interior being utilized for arrangement of a vertical drive chain which extends vertically in and outside the post. The vertical drive chain is connected to the vertically movable carriage.
According to this known arrangement, load transfer between the rack and the crane is carried out by a combination of horizontal movement of the crane on a predetermined track extending along the front of load-in/load-out sections of the rack, vertical movement of the carriage, and lateral stretch and retraction of a load transfer device. For this purpose, upward and downward movement of the vertically movable carriage is performed by the vertical drive chain being driven to run. The first guide rollers for inhibiting longitudinal oscillations and second guide rollers for inhibiting lateral oscillations are guided along the guide rail portions, whereby the vertically movable carriage can be moved upward and downward while being prevented from longitudinal and lateral oscillations.
According to such known arrangement, the vertical drive chains, positioned outside the posts and connected to the ends of the vertically movable carriage, are positioned close to the outer sides of the respective posts. Therefore, the vertical drive chains tend to sway back and forth during their run and may impinge upon outer surfaces of the posts. To avoid such an occurrence, the pair of posts may be sufficiently spaced from each other so as to allow the vertical drive chains to be positioned away from the outer surfaces of the respective posts, whereby the chains can be prevented from colliding with the outer surfaces of the posts. In this case, however, some adverse effect may be caused to the structural aspect of various parts of the crane.
In place of the vertical drive chain, other kind of cord element, such as wire rope, may be used to drive the vertically movable carriage for upward and downward movement. However, in that case, too, a similar problem is likely to occur.
According to the above described prior-art arrangement, the second guide rollers for inhibiting lateral oscillations are dimensionally so designed as to produce a clearance in relation to at least one side of the open-groove shaped guide rail portion, since smooth guidance through free rotation of the rollers cannot be effected if the rollers simultaneously come in contact with both sides of the guide rail portion. The presence of this clearance is a cause of jolting during a load transfer, in particular, in which the fork of the load transfer device is stretched and retracted. This does not permit any smooth and accurate load transfer, and may even result in generation of large noise when operation is carried out at high speed. Such jolting will also occur during upward and downward movement of the vertically movable carriage.
The first guide rollers for inhibiting longitudinal oscillations are each held in contact with the bottom of the corresponding guide rail portion by the resilient force of the spring and, therefore, they can absorb any surface irregularity of the guide rail portion to maintain the carriage constantly in a jolting-free condition. In this case, however, the second guide rollers for inhibiting lateral oscillations as mounted to each movable shaft are caused to shift in unison with the first guide rollers in the direction in which the first guide rollers are biased for surface contact, and this results in a lateral pressure being exerted on the second guide rollers. As a consequence, the second guide rollers are liable to some frictional wear which will in turn unfavorably affect the environment due to dust generation and will further enlarge the above mentioned clearance.